Encased heating unit



c. M. OISTERHELD 2,360,267

ENCASED HEATING UNIT Oct. 10,1944.

2 Sheets-Sheet 1 Filed Nov. '23, 1942 INVENTOR.

CLARK (Jam-wan BY 1 727 g ATTORNEY Oct. 10, 1944. q QSTERHELD 2,360,267-

ENCASED HEATING UNIT Filed Nov. 25. 1942 Y 2 Shets -Sheet 2 4a Ff INVENTOR CLARW Osrmmp ATTQRNEY I Patented Oct 10,1944

-01: M. Osterheld, summsn, Wis., assignor to McGraw Electric Company, Elgin, 111., a corporation of Delaware Application November 23, 1942, Serial No. 460,837 4 Claims. 3 (01. 201-47) My invention relates to electric resistor and electric heating units.

Among its objects are:

To provide a relatively simple and inexpensive encased resistor or heating unit having a minimum number of parts; to provide a resistor or heating unit having a relatively thin inorganic,

electric-insulating layer between the resistor and Y the outer casing; to provide a heating-unit having a relatively small heat storage mass; to provide a heating unit so designed and constructed that the resistor conductor can be operated at relatively low temperature to thereby provide a heating unit which will have a long life; and to provide a heating unit that will have a relatively high breakdown voltage and that shall permit of being formed into any suitable or desired shape for application to a device or mass to be heated.

Other objects of my invention will either be apparent from a description of my invention as embodied in several modifications or will be pointed out in the course of such description and It forth in the appended claims.

In the drawings,

Fig. 13 is a view in side elevation of a further modification of a resistor conductor which I may utilize, and,

Fig. 14 is an end view of the element shown in In general my invention disclosed and claimed in the instant application comprises an outer tubular casing member it which, while preferably made of metal, can be made of any other suitable high-temperature-resisting and heat-transmitting material. I mayv mention that among the'metals I may use is aluminum, particularly because I desire to provide on the inner surface of the casing 2| a coating 23 having an inorganic, coherent, integral, heat-conducting, high temperature-resisting and electricinsulating characteristic and I have found that aluminum may-have provided thereon by means Figure 1 is a fragmentary perspective view of an outer tubular casing forming a part of the device embodying my invention,

Fig. 2 is a view, in side elevation, of a convoluted resistor strand,

Fig. 3 is an end view thereof, Pig. 4 is a fragmentary perspective view of a partially assembled resistor or heating unit,

Fig. 5 is a fragmentary perspective view of an assembled resistor or heating unit,

l'ig. 8 is a fragmentary perspective finished resistor or heating unit, j l

Fig. "l is a fragmentary perspective view of another form of resistor conductor in its initial shape and in partly finished condition,

Fig. 8 is a perspective view thereof shown in an intermediate and further .stage of construcview of a Pig. 9 is afragmentary perspective view of the ame'mbly of an outer tubular casing and the resistor conductor of Fig. 8,

Fig.1!)isaperspectiveviewoi?afurtherimdi-v .The main consideration as to the coating is that now well known in the art, such a coating. Reference may be had to Patent No. 1,526,127 for a method of providing such a coating, usually called an anodic" coating although such c0at-. ing. may be provided by other means now, well known in the art.

Preferably the thickness of such a coating is verysmall and may be on the, order of .0001" and even up to .001" and I amnot limited to any particular or definite thickness of such coating since various methods now well known in the art result in coatings of different thicknesses.

it shall have a relatively high electric-insulat ing characteristic so that there will be a wide margin of safetywith regard to the break-down voltage. Further, a coating of this kind should permit of changing the shape of the heating unit so that it can be adapted to cooperative relation with a piece of apparatus or a mass 'of material .to be heated. "This, of course, means that the coating, at least at some of its part, will be, subjected to bending stresses and it is, of

'fication of resistor conductorwhich I may'use shown in partly completedcondition,

Fig. 11 is a perspective view of the resistor conductor of Fig. 10 shown in further intermediate stage of manufacture,

Fig. 12 is a fragmentary perspective view of an outer casing with the resistor conductor of Fig. 11 located therein,

course, desirable that the coating shall not be damaged to any appreciable extent.

I desire to locatewithinthe casing It a re- 'sistor member and I have shown a small strip or strand 2b of any suitable ,9; desired kind of resistor in Figs. -2 and 3 of the drawings. I

have there shown the strand 2! as wound to substantially helical-coil shape' and as shown, the" wider surface of the strand constitutes the outer periphery of each turn for a reason that will hereinafter appear. The material orthe resistor may be Nichrome or I may use aluminum or aluminum alloy,

' Referring tol'ig. of the drawings, I have there illustrated an electric resistor or heating unit embodying my invention in its intermediate stage of assembly or manufacture and this figure shows a casing 2| having located therein the helically-coiled resistor member 25.

Any suitable or desired method of efiecting location of the helically-coiled conductor 25 in the casing 2| may be employed and I may merely mention that it is easily possible to effect a further winding up of the helical coil into which conductor 25 is shown as having been formed, in

. the casing. To permit of assembling the heating unit as described shows, a certain amount of springiness or resilience is left in the resistor during its manufacture.

I provide further a separator 217 in the shape or a relatively thin strip of metal, preferably of aluminum, although it may also consist of some other metal on. the entire surface. of which the hereinbefore described kind of coating has been provided as above described.

Fig. 5 of the drawings shows the separator 2? completely inserted in the outer casing 2i and the helical-coil conductor 25 therein, preparatory to subjecting the assembly to a heavy extemallyapplied pressure, the final result being shown in Fig. 6 or the drawings. The greater part oi the peripheral wall of the casing 2H is now positioned in two layers substantially parallel with each other and the turns of the helically-coiled con= ductor 25 are positioned in two layers substan tially parallel with each other and spaced apart by the separator 27. For illustrative purposes only I may make the thiclmess of the separator Ell on the order of .025" or even appreciably less than this dependent upon other conditions present in the assembly.

Referring now to Fig. 7 of the drawings, 1 have there illustrated a conductor it of a kind already used heretofore in resistor and heating units. The resistance conductor was originally in the shape of a strip of resistance material or metal such as Nichrome of a thickness and a width which, taken in connection with a plurality oi laterally-extending slots alternately extending out to the respective edges, will give the desired length and area of current flow path. Fig. 8 of the drawings shows the conductor 29 after having been shaped into substantially circular form as seen laterally thereof, there being a slight gap 3| between the opposing, edges. This conductor has an inherent resilience or springiness as hereinbefore described for conductor 25.

Fig. 9 shows the outer casing 2| having positioned thereinthe convoluted conductor 29 it being understood that any suitable means for eilecting temporary compression of .the curved conductor 29 so that the small longitudinal gap 3| has become substantially zero, to permit 0! easy and quick insertion of the conductor 29 in the casing 2|, after which removal of the compressing means will permit the conductor 29, because of its own inherent resilience or springiness, to engage the inner coated surface of the casing 2| over substantially the entire periphery.

Referring now to Fig. 10 of the drawings, I have there shown a still further modification of a resistor conductor which comprises a wire 33 bent to include short substantially parallel and laterally-extending convolutions. Fig. 11 shows the conductor 33 when it has been shaped as on a suitable mandrel or a rod to substantially circular form laterally thereof with the end connecting portions of the adjacent convolutions out of engagement with each other. Fig. 12 shows the conductor 33 as positioned in a coated outer casing 2|, the same method of effecting insertion of the convoluted conductor 33 having inherent resilience or springiness, into the casing 2| having been embodied substantially as set forth for the modification shown in Figs. 7, 8 and 9.

Figs. Band 14 showing still further modification of a resistance conductor, as a wire 35 wound into helical-coll shape and the same comments as made hereinbefore in connection with the conductor shown in Figs. 2 and 3 will also apply to conductor 35.

It is to be understood that the structures shown in Figs. 9 and 12 respectively are not in the final shape, but that the next step in the completion of the manufacture of such resistor or heating unit is the insertion of a separator 21 within the conductor 33, 35 or 29 and the subjection of these parts to a compression force resulting in a fiattened heating unit.

It is obvious that the details of the design, construction and manufacture of a heating unit embodying my invention are such that when finished, as shown for instance in Fig. 6 of the drawings, the flattened outer tubular casing will have been compressed to such an extent that it will hold the conductor member inclose operative and compressing engagement on the separator and with its own inner surface whereby a good heatflow path is provided.

It is obvious that the coated inner surface of the casing 26 and the coated surface of the sepa-= rator 23 will provide electric insulation between the outer casing and the conductor and between the two layers of the conductor. However, if desired, I may utilize an aluminum resistor conductor or an aluminum alloy and in this case the entire surface of the aluminum resistance condoctor may have provided thereon an anodic coating of the kind hereinbefore described. The result of this construction will be that there will be a greater factor of safety against breakdown between. the conductor and the casing than would otherwise be the case.

As above stated, the thickness of the electricinsulating coating is relatively very'small and since it; is heat-conducting and high-temperature-resisting, the length of heat flow path through the dielectric layer, that is, through the coating or coatings, will be relatively very small and will be practically unafi'ected by repeated heating and cooling of a heating unit made according to the present invention.

As above stated, the electric-insulating coating should be able to withstand change of form of the part with which it is associated and this will permit of changing the general contour of the outer tubular casing 2| in order to adapt it to any desired appliance or mass with which a heating unit-of this kind is to be closely operatively associated.

Various modifications may be made in the structures embodying my invention as shown and described herein and all such modifications clearly coming within th scope of the appended claims are to be considered as being covered thereby.

I claim as my invention:

1. An encased flat resistor unit comprising an elongated fiat, convoluted two-layer metal resistor member, a thin metal separator between the two layers of said resistor member and a fiat tubular metal casing around the two-layer resistor member in tight clamping engagement thereagainst-,1the entire outer surface of the metal separator and the inner surface of the metal casing having thereon an integral, inorganic, heat-conducting, high temperature-resisting and electric-insulating coating, the thickness ofsaid I coating being less than .001.

2. An encased flat resistor unit comprising an elongatedflat convoluted two-layer metal resistor member, a thin metal separator having electricinsulating characteristics located between the two layers of said resistor member and a flat tubular metal casing around the two-layer resistor member in tight clamping engagement thereagainst, the entire outer surface of the metal separator and the inner surface of the metal casin; having thereon an integral, inorganic, heatconducting, high temperature-resisting and electric-insulating coating, the thickness of said coatinabeinglessthanml.

3. An encased flat resistor unit comprising an elongated fiat convoluted two-layer metallic resistor member, a thin fiat metal separator between the two'layers of said resistor member and a flat tubular metal casing around the two-layer resistor member holding the resistor member in I close heat-transmitting engagement with itself and with the separator, the inside surface of the casing, the surface of the resistor and of the separator having thereon an integral, inorganic,

heat-conducting, high temperature-resisting and thin metal separator strip between the two layers of the resistor conductor and a flat tubular casing around the two-layer resistor conductor holding the latter in close heat-transmitting engagement withthe casing and with the separator.

CLARK M. os'raarram. 

